2wd to 4wd conversion on a 77 Ford F-150?

So I'm getting an old 77 ford from my buddy for about $700. I planned to do a restoration, but I put some thought and might throw abit of some modifications to it because since it's stock height, carburated and 2WD, I'm automatically gonna have trouble during the winter. My friends and I have been talking about a 4wd conversion, I've seen people do it with Leaf springs. And I've read that they fabricated the frame to make it 4wd capable. But I don't have a welder nor the experience of welding so I really don't wanna mess anything up. So my main question is, is it possible to do the swap for the 2wd to 4wd without cutting into the frame? It's a 77 ford f150 but what I don't know is if they changed up the frames of the 2wd and 4wd. It sounds a little confusing because it's alittle confusing for myself. But it'd be great If I know what I should do.

It is possible, but without experience welding and fabricating, your $700 truck will turn into a $7,000 project fast.

Stop right there. Plan on robbing a bank first to pay for this. You can't just throw a front axle on there because the gear ratio has to match up with the rear axle ratio, somewhat. (The transfer case determines the final gear ratio in the front) Then you need the shift linkage up through the floor and most likely different front springs ( heavier). Your biggest project is getting BOTH axles turning the same speed going down the road. You can't have one axle turning slower / faster than the other.